The semiconductor industry has experienced rapid growth due to improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from shrinking the semiconductor process node (e.g., shrink the process node towards the sub-20 nm node). As semiconductor devices are scaled down, new techniques are needed to maintain the electronic components' performance from one generation to the next. For example, low gate-to-drain capacitance and low on resistance of transistors may be desirable for power applications. In addition, it is desirable to integrate vertical power transistors with lateral power transistors on a same semiconductor die.
As semiconductor technologies evolve, metal oxide semiconductor field effect transistors (MOSFET) have been widely used in today's integrated circuits. MOSFETs are voltage controlled devices. When a control voltage is applied to the gate a MOSFET and the control voltage is greater than the threshold of the MOSFET, a conductive channel is established between the drain and the source of the MOSFET. As a result, a current flows between the drain and the source of the MOSFET. On the other hand, when the control voltage is less than the threshold of the MOSFET, the MOSFET is turned off accordingly.
MOSFETs may include two major categories. One is n-channel MOSFETs; the other is p-channel MOSFETs. According to the structure difference, MOSFETs can be further divided into two sub-categories, namely trench power MOSFETs and lateral power MOSFETs. In an n-channel trench power MOSFET, a p-body region is employed to form a channel coupled between the source region formed over the p-body region and the drain region formed under the p-body region. Furthermore, in the trench power MOSFET, the drain and source are placed on opposite sides of a wafer. There may be a trench structure comprising a gate electrode formed between the drain and the source of the trench power MOSFET.
Trench power MOSFETs are commonly known as vertical power MOSFETs. Vertical power MOSFETs have widely used in high voltage and current applications due to their low gate drive power, fast switching speed and lower on resistance.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.